I have a special tool that I built almost 2 decades ago specifically designed to aid in the design of passive solar structures, and you see it right in the center of this photo. It's as valuable as any other drawing tool I use in the early stages of design. As you all know by now I start my designs the old fashioned way - pencil and paper - before I go moving to computer aided modeling. Often, especially with really complex designs, I have to go back and forth between the two, but that's a discussion for another time. For this essay I want to sing the praises of this handy little model you see in the picture.
The one you see here is designed for about 35º N. Lat. (Albuquerque/Santa Fe area) and it shows the course of the sun at the Solstices and Equinoxes. Creating a Passive Solar design (not to mention great daylighting within any structure) means working with and calculating the various positions of the sun throughout the day and throughout the year. On my first passive solar project it became quickly apparent that I needed a quick reference to estimate sun angles while starting design on a landscape. I needed to know the sun's various positions throught any given point in the year in terms of azimuth, altitude, angle, sunrise & sunset positions on the horizon, and everything in between. So, I set to making this model. It's been exceptionally helpful and something I use constantly (as you can tell from it's worn condition). I pull it out now and then to show clients how drastically the sun's position actually changes throughout the year. Today I was looking down at it on my current drawing and couldn't resist sharing it with you all.
The flat circular disc base is a representation of all 360º of the horizon as if you stood in one place and turned around in a full circle. There is a central arch and then 3 other arches that cross the central arch. The central arch represents due North and South. The other 3 arches represent the course of the sun as it rises and sets from East to West at different times of the year. The highest arch at the top shows the course of the sun during the Summer Solstice. Notice how much more of an arch it has than the others showing how much longer the day is in summer and how high and direct the sun is, which of course is what makes things seasonally warmer that time of year. The middle arch is the Autumn and Spring Equinox path of the sun. The lowest arch is the Winter Equinox arch. See how much smaller the arch is representing the shorter days of the winter. Also, you'll see that winter's sun angle is not nearly as direct as it is during the summer and that indirect angle of light is actually what is causing the winter to be colder as well as the deminished daylight hours that time of year. Fun fact, in our orbit around the sun, in the Northern Hemisphere we are actually closer to the sun in winter. It's actually the lower angle of the sun in winter that makes it so much colder. Lastly, notice also how much the sun's rising position changes along the horizon at sunrise and sunset at various points of the year. The point along the horizon where the sun rises and sets is vastly different from summer to winter. Ancient cultures were keenly aware of this and designed structures like those seen at Stonehenge and Chaco Canyon that responded in precise alignments to the knowledge represented in this little model. If we are to live in a built world that lives in harmony with it's place on earth, the importance of designing buildings that respond to natural alignments, natural lighting, natural changing courses of the seasons is as vital now as it was in ancient times.
So as you can see, designing a passive solar building or really any building that wants to consider daylighting is tricky and calculating business. However, with the right tool, one can make informed, accurate and rapid decisions during the design process. If the tool you need doesn't exist, then design and make that first.
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